Method and apparatus for wood chip pasteurization

ABSTRACT

A method and apparatus for pasteurizing comminuted wood. A housing is substantially sealed over the hatch of a ship&#39;s cargo hold before it is opened. The hold contains comminuted wood for transport, which are typically contaminated with pathogens that it is desired to destroy. Hot water is provided to combine with the comminuted wood to form a slurry. The slurry is pumped to a pasteurization vessel where it is held for a predetermined pasteurization temperature and time. Subsequent to the predetermined pasteurization time, the slurry exits the pasteurization vessel and the water is reclaimed from the wood chips. The reclaimed water is preferentially reused to slurry more chips. The method and apparatus preferably include employing an air removal and cleaning system which maintains the environment within the cargo hold at conditions tolerable for a worker to work therein, the air removal and cleaning system purifying the air obtained therefrom before exhausting it into the atmosphere.

BACKGROUND OF THE INVENTION

This invention relates to methods and apparatus for ridding wood chips,particularly imported wood chips, of pathogens such as insects,nematodes and fungi. More particularly, the invention pertains to suchmethods and apparatus employing hot water for pasteurization and fortransport of the wood chips from a vessel, for example a ship, and anair circulation system to prevent escapement of pathogens.

Imported wood fiber of any sort and imported wood chips in particular,hereinafter referred to as "comminuted wood," pose a health threat todomestic plant species in potentially carrying pathogens from a site oforigin to a site of delivery. Typically, poisonous chemicals such asaluminum phosphide or methyl bromide have been used for fumigation ofimported wood fiber such as wood chips. However, such treatmentchemicals cannot penetrate wood chips or large containers adequatelywithin reasonable time. In addition, poisons are expensive to apply andmust be handled and disposed of with utmost care. In addition, methylbromide has been implicated by the Environmental Protection Agency incontributing to ozone depletion and its use is controversial. There is,generally, a conflict between the ability of a poison to function and tobe harmless to the natural environment.

Attempts to employ a non-toxic and environmentally compatible agent forexterminating insects include utilizing an inert freezing liquid, suchas liquid nitrogen, as proposed for example in Tallon, U.S. Pat. No.5,165,199. However, the method of Tallon is employed for relativelysmall areas and volumes, as liquid nitrogen can be prohibitivelyexpensive in large quantities. Moreover, liquid nitrogen must generallybe kept away from structures or articles that it is desired should notbecome brittle in view of stresses placed thereon. In addition, afreezing agent may not be effective against some pathogens, such aseggs, spores and seeds.

Pasteurization has long been used to treat food products, particularlymilk products, and it has even been proposed in Roth et al., U.S. Pat.No. 5,372,149 to pasteurize snuff. In the particular process of Roth, itis proposed to cook snuff in a steam jacketed vessel with stirring plowsto bring the snuff into contact with the heated walls.

While pasteurization has been employed in articles for human ingestion,it has apparently not been proposed to employ such a process in thetreatment of wood chips. In particular, it has not been previously knownhow to apply such a process in the treatment of imported wood chips,which are generally delivered to a delivery site in extremely largequantities in a ship's cargo hold, where it is desirable to prevent theescape of pathogens to the local environment.

Accordingly, there is a need for a novel and improved method andapparatus for wood chip pasteurization that pasteurizes wood chips priorto exposure to the local atmosphere and which is relatively inexpensive,non-toxic and environmentally compatible.

SUMMARY OF THE INVENTION

The method and apparatus for pasteurizing wood chips of the presentinvention solves the aforementioned problems and meets theaforementioned needs by employing a housing which is set upon andsubstantially seals the hatch of a ship's cargo hold in which wood chipsare held, the housing being connected to an air removal and cleaningsystem, and employing an inlet to the hold for hot water and an outletfor a slurry, the slurry being a combination of the wood chips and thehot water.

The air removal and cleaning system controls the temperature within theship's hold and provides fresh air so that a person may work therein todeliver the wood chips to the slurry conveying system. Preferably aswell, the air removal and cleaning system maintains a slightly negativeair pressure within the housing which, along with the seal, helps toprevent pathogens from escaping into the atmosphere.

The hot water outlet of the hot water system is fed into the inlet ofthe slurry conveying system into which wood chips are also fed by thehuman operator aided by a machine, e.g., a clam-shell or bucket, tocreate the slurry. The slurry is pumped through a sealed pipe feeding aremotely located pasteurization vessel wherein the slurry is depositedat the top and is pumped from the bottom. The slurry is caused to beheld in the vessel at

a predetermined minimum pasteurization temperature, determined by thehot water temperature, for a predetermined minimum pasteurization time.Subsequently, the slurry is pumped from the pasteurization vessel anddrained, and the remaining wood chips are output from the system forcollection and transport.

Water drained from the slurry is collected, reheated as necessary toreach the temperature required for the process, and recirculated toproduce the slurry. Waste heat may be used to reheat the water.

Therefore, it is a principal object of the present invention to providea novel method and apparatus for pasteurizing wood chips.

It is another object of the present invention to provide such a methodand apparatus that isolates wood chips from the local atmosphere andpasteurizes the wood chips before exposure to the local atmosphere.

It is still another object of the present invention to provide such amethod and apparatus that is relatively inexpensive.

It is a further object of the present invention to provide such a methodand apparatus that does not rely on toxic substances.

It is still a further object of the present invention to provide such amethod and apparatus that is environmentally compatible.

The foregoing and other objects, features and advantages of the presentinvention will be more readily understood upon consideration of thefollowing detailed description of the invention, taken in conjunctionwith the following drawing.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE is a schematic of a method and apparatus for pasteurizingwood chips according to the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Referring to the Figure, a method and apparatus ("the system") forpasteurizing wood chips 10 is shown. The system pertains to pasteurizingwood chips that are held in the cargo hold 16 of a sea-going vessel 2.The vessel 2 has an upper decking surface 4 which has an opening 6therethrough for accessing the cargo hold. Around the opening 6 is ahatch 14 which covers and protects the opening 6 and is adapted to openupwardly (as shown).

The wood chips are held in the cargo hold to prevent the escape ofpathogens to the external atmosphere. However, when opening the hatch atthe port of entry of the vessel, the chips normally become exposed tothe local atmosphere. To prevent this, a housing 12 is provided forremovable placement over the opening 6 and the hatch 14. Preferably, thehousing is placed over the hatch at the site of delivery of the woodchips before opening the hatch, so that the wood chips may be rid ofpathogens before being exposed to the local atmosphere.

The housing sits on the upper decking surface 4 as shown in the Figure.The housing is large enough to permit the hatch 14 its full range ofopening when the housing is set thereover, and to provide room forworkers and machinery, such as cranes and bulldozers, to fit inside andoperate on the comminuted wood, to unload the wood from the vessel andtreat it on shore as described more fully below.

During shipping, micro-organisms acting on the wood chips 18 typicallycreate an oxygen poor environment within the hold 16, in which thetemperature is typically about 140 degrees Fahrenheit and the humidityis nearly 100 percent. It is desirable to neutralize this hostileenvironment to permit the workers to work within the housing and thehold. For this purpose, the housing is adapted for sealing around thehatch 14, through contact with the upper decking surface 4, to preventthe escape of pathogens from the hold.

In support of this purpose an air removal and cleaning system 24 isprovided. The housing 12 is connected to the air removal and cleaningsystem at output manifold 20. A filter 42 is provided for removingentrained organisms and particulates from the air. Fan 39 transfers theair through the filter 42. The air passing through the filter is thenexpelled into the atmosphere through an atmospheric air outlet 46.

In addition, air removed from the hold 16 through the manifold 20 may betreated with water to remove a large portion of the particulates priorto filtering. Hot water may be employed to pasteurize the airborneparticulates. The air is transferred through a hot scrubber 38 to thefilter 42, the hot scrubber contacting hot water with the air. Hot wateris provided at inlet 37 and expelled at outlet 41 as described below.

The air removal and cleaning system 24 maintains a slightly negative airpressure in the hold 16 to prevent the escape of pathogens into theatmosphere. The air removal and cleaning system 24 preferably alsoreceives air from a pasteurizing vessel 50 via conduit 45 for cleaningair within that vessel. Although adequate fresh air for personnelworking within the vessel would ordinarily leak into the vessel due tothe negative pressure therein, an air inlet 22 may be provided to supplyfresh air.

The hopper 19 is connected to an input manifold 26 of a hot watercirculation system 28, the hot water being circulated through the hopper19 and being output at a manifold 30 of the hot water circulation system28.

The wood chips 18 are fed into the hopper 19 of the hot watercirculation system 28 by an appropriate means, such as a bulldozer 17and crane 15. The wood chips 18 combine with the hot water provided bythe hot water circulation system 28 to form the slurry 34.

The slurry 34 is pumped through a sealed pipe 48 by pump 49 feeding aremotely located pasteurization vessel 50. The slurry is deposited atthe top of the pasteurization vessel to form a bed of chips 35, which ispumped as a slurry from the bottom of the vessel 50 by a pump anddischarge device 51, whereby the pasteurization vessel acts as afirst-in-first-out ("FIFO") storage container.

The pasteurization vessel 50 maintains the hot slurry so that it is heldat or above a predetermined minimum pasteurization temperature T1, thetemperature T1 preferably being about 180 degrees Fahrenheit.Preferably, the temperature in the pasteurization vessel 50 ismaintained passively, through the use of appropriate insulating materialwhich contains the heat of the slurry. Moreover, the rate at which theslurry 34 is pumped through the pasteurization vessel 50 is controlledso that the time of transit of the slurry through the vessel 50 duringwhich the temperature is at or above the temperature T1 is apredetermined minimum pasteurization time "t", the time "t" preferablybeing about 75 minutes.

Although only one pasteurization vessel 50 is shown, it is to berecognized that two or more such vessels may be used. In particular,multiple pasteurizing vessels may be used to avoid "rat holing"; thatis, to ensure that the slurry flows uniformly through the pasteurizationvessel or vessels.

Slurry 34 exiting the pasteurization vessel 50 is pumped downstream bythe pump and discharge device 51 to a water separator 52 wherein most ofthe water is drained off at drain pipe 54. The remaining wet wood chipsare placed in a chip pile 56 to await collection and transport.

Preferably, water from the system 10 is reclaimed for recycling throughthe system. Water drained from the water separator 52 is preferentiallysent to a heating system 64 via a stand pipe 58. Any excess water fromthe drain pipe 54 above what is immediately demanded by the processoverflows through pipe 59 into a surge tank 60. Any dearth of waterbelow what is immediately demanded is made up from the surge tank 60.

Recirculated hot water is supplied to the scrubber 38 via inlet 37 andreturned via outlet 41 to the stand pipe 58. Drainage and rain waterfrom the chip pile 56 collected on pad 53, which may be made e.g., ofconcrete or black top, are pumped to the surge tank 60 by pump 61. Afresh water inlet 62 is provided for replacing lost water, primarily asa result of evaporation from and absorption into the wood chips.

The hot water circulation system 28 also employs the heating system 64for heating the water to a predetermined temperature T2. The temperatureT2 is high enough so that, combined with the chips, the resultingtemperature of the mixture will be at a predetermined designtemperature, e.g., about 188 degrees Fahrenheit. The water may be heatedby a hot water heater 70.

The heating system 64 of the hot water circulation system 28 may employwaste heat. The waste heat may be obtained, for example, by a heatexchanger, such as tubular coils 68, coupled to a supplementary heatsource 72. In that event, the hot water heater 70 provides heat whensufficient waste heat is not available.

While the waste heat source 72 may be located some distance away,thereby requiring a pump 73, the water heater 70 is preferably locatednear the water separator 52. The stand pipe 58 is preferably high enoughthat water will flow by gravity through the water heater 70 and into thehopper 19.

It is to be recognized that, while a specific method and apparatus forpasteurizing wood chips has been shown as preferred, otherconfigurations could be utilized, in addition to configurations alreadymentioned, without departing from the principles of the invention. Inparticular, pasteurizing of wood chips may be accomplished without theair circulation system, and by employing other means of providingthereto and subsequently reclaiming therefrom a heated fluid for apredetermined time.

The terms and expressions which have been employed in the foregoingspecification are used therein as terms of description and not oflimitation, and there is no intention of the use of such terms andexpressions of excluding equivalents of the features shown and describedor portions thereof, it being recognized that the scope of the inventionis defined and limited only by the claims which follow.

We claim:
 1. A method for preventing the spread of pathogens fromcomminuted wood delivered in a shipping container in which thecomminuted wood is isolated from the local atmosphere to substantiallyprevent the escape of pathogens therefrom, comprising:mixing thecomminuted wood with a liquid inside the shipping container to form aslurry for transporting the comminuted wood to a location outside of theshipping container; transporting the comminuted wood to the location byflowing said slurry from the inside of the shipping container to thelocation while said slurry remains isolated from the local atmosphere tosubstantially prevent the escape of pathogens therefrom; and maintainingsaid slurry at or above a predetermined, elevated temperature for atleast a predetermined time at said location while said slurry remainsisolated from the local atmosphere to substantially prevent the escapeof pathogens therefrom, to pasteurize the comminuted wood.
 2. The methodof claim 1, wherein said liquid is water, the method further comprisingheating said water prior to mixing with the comminuted wood.
 3. Themethod of claim 1, further comprising providing a holding vessel formaintaining said slurry at said predetermined elevated temperature forsaid time at said location.
 4. The method of claim 3, further comprisingheating said liquid prior to mixing with the comminuted wood.
 5. Themethod of claim 3, further comprising continuously forming andtransporting said slurry to said holding vessel and continuouslyreleasing said slurry from said holding vessel on a first-in-first-outbasis to maintain said slurry at or above said predetermined elevatedtemperature for at least said predetermined time.
 6. The method of claim5, further comprising separating said liquid from said slurry afterreleasing said slurry from said holding vessel, to recover thecomminuted wood.
 7. The method of claim 6, further comprising recyclingsaid liquid after releasing said liquid from said slurry to form saidslurry.
 8. The method of claim 7, further comprising heating said liquidprior to forming said slurry.
 9. The method of claim 8, wherein saidheating of said liquid is by using waste heat obtained from otherindependent processes.
 10. The method of claim 1, wherein the shippingcontainer has an opening the method further comprising placing a coverover the opening and providing a liquid inlet and a slurry outlet fromoutside the container to inside the container.
 11. The method of claim10, wherein said cover comprises a housing providing room for machineryand personnel to mix said liquid with the comminuted wood within thecontainer.
 12. The method of claim 11, further comprising allowing freshair into said housing and removing existing air from within saidhousing, filtering said existing air, and releasing said existing airinto the local atmosphere.
 13. The method of claim 12, furthercomprising removing said existing air from said housing at a rate whichmaintains negative pressure within said housing.
 14. A method forpasteurizing comminuted wood, comprising:combining a heated fluid withthe comminuted wood at a first location to form a slurry; pumping saidslurry from said first location to a second location; maintaining saidslurry at said second location at or above a predetermined temperaturefor at least a predetermined time sufficient to pasteurize thecomminuted wood; and thereafter separating said heated fluid from saidslurry to recover the comminuted wood.
 15. The method of claim 14,further comprising recycling said fluid obtained from said step ofseparating to form said slurry.
 16. An apparatus for use in preparing totransport comminuted wood from a sea-going vessel to a receptacleon-shore for pasteurizing the comminuted wood, the sea-going vesselhaving an opening through an upper decking surface thereof, the openingproviding access to a cargo hold disposed beneath the upper deckingsurface, the opening being covered by a hatch door, the apparatuscomprising a housing adapted to be disposed over said opening and saidhatch door, and on the upper decking surface of the sea-going vessel,said housing being further adapted so that said hatch door can be fullyopened upwardly while said housing is set on the upper decking surface,said housing adapted for sealing with the upper decking surface tosubstantially prevent the passage of air from the cargo hold to theexternal atmosphere, wherein said housing is connected to an air outletfor removing existing air from said cargo hold through said air outlet.17. The apparatus of claim 16, wherein said air outlet is part of an airtransfer system which includes a filter in communication with said airoutlet.
 18. The apparatus of claim 16, wherein said air outlet is partof an air removal and cleaning system which includes a hot scrub incommunication with said air outlet for bringing said existing air incontact with a hot liquid.
 19. An apparatus for use in preparing totransport comminuted wood from a sea-going vessel to a receptacleon-shore for pasteurizing the comminuted wood to substantially preventthe spread of pathogens to the local atmosphere, the sea-going vesselhaving an opening through an upper decking surface thereof, the openingproviding access to a cargo hold disposed beneath the upper deckingsurface, the opening being covered by a hatch door, the apparatuscomprising a housing adapted to be disposed over said opening and saidhatch door, and on the upper decking surface of the sea-going vessel,said housing adapted for sealing with the upper decking surface tosubstantially prevent the passage of air from the cargo hold to theexternal atmosphere.
 20. The apparatus of claim 19, wherein said housingis connected to an air outlet for removing existing air from said cargohold through said air outlet.
 21. The apparatus of claim 20, whereinsaid air outlet is part of an air removal and cleaning system whichincludes a hot scrub in communication with said air outlet for bringingsaid existing air in contact with a hot liquid.